When I was a kid, I used to have a toy car that was better than everyone else's. It wasn't that it was flashier or more exotic, it was just a well-proportioned little Matchbox car, a bit chipped and well-used. What made it different was that I pretended it had a massively powerful engine under the bonnet. There was no way my mates could prove it didn't.

I can't remember what it was but it looked a bit like this model of an Audi RS 5 I have here beside me – boot, bonnet, wheels, that sort of thing. The thing is, I don't have to pretend its better than anyone else's toy car. I've driven the real RS 5 and I can tell you now, it really does have a massively powerful engine under the bonnet.

Given that it has a 4.2-litre, normally-aspirated V8 petrol engine, pushing a stonking 444bhp into the tarmac through all four wheels, and it's capable of reaching 62mph in a blistering 4.6 seconds, you'd think Audi would have been justified in making something a bit more . . . well, extreme-looking. I mean, it's quicker than an Aston Martin Vantage or a Maserati GranTurismo and only the merest fraction slower than a Ferrari F430.

But no. The wheelarches of the RS 5 are but gently flared to accommodate the 19" alloys shod with 265/35 R tyres, the bonnet has no power hump, the tail has no massive wing, the spoiler under the chin is a coherent part of the nose, the lights are squared off and narrow and the big grille is just the Audi trademark.

There's no doubt this new coupé is an elegant, well-proportioned car with a long and tapering cockpit on top of an uncluttered body, but it's an understated elegance. To the uninitiated, only two things make the RS 5 stand out from the herd as it moves along the motorway: the speed with which it overtakes the beasts further down the food chain, and the great trumpeting sound that accompanies the manoeuvre.

To those of us lucky enough to be initiated, this is a quattro coupé in the finest tradition and one well worthy of the RS moniker. It has twin oval exhaust ports at the rear, the suspension is 20mm lower than on the standard A5 and the air intakes at the front gape wider. Those who look closely will see there's a small tail spoiler that normally lies flat in the boot lid, but which rises at 75mph to help keep the car stable at higher speeds. Given that the top legal speed in the UK is 70mph, you may as well have a little sign under it that reads, "I'm now breaking the law".

The RS 5 only comes with the S tronic gearbox in which the seven forward gears can be selected either fully automatically, or manually using either the left and right paddles under the steering wheel or the shift knob to shunt sequentially through the cogs.

Audi has this drive select thing whereby you can choose to have the car set up for four types of driving, simply at the stab of one button. It adjusts the stiffness of the suspension and steering and it changes the gearshift characteristics. You can let it think for itself and choose the best set up for you automatically, you can tailor the settings for yourself, or you can choose comfort or dynamic mode. On some makes the changes in response are marginal. Not so here.

Through town, along the byways and probably on the motorways, the Comfort mode makes most sense. Bumps on the road come and go with the minimum of acknowledgement from your butt, the steering is light but accurate and gears change at relatively low engine speeds. We're told you can get an average fuel consumption of 26.2mpg in this mode.

But once you're out on the moors or up in the mountains, you should cycle the options through to Dynamic where everything gets a lot more exciting, if a bit more expensive. The suspension now has all the pliancy of a quality piece of sprung timber, the steering has noticeable stiffened up in your grip, and the engine is roaring well up through the optimum power band before the gears are allowed to change in automatic mode. Even the exhaust note sounds like it's been tuned to be more sonorous at low speeds, and to bark brighter at high. Using the paddles to shift between gears makes it even better with swift, smooth changes and that glorious brap of an exhaust note while the cogs are lining up. All in all, turning it to Dynamic mode is literally like getting into a different car.

The RS 5 is described as a practical as well as performance car, and fair enough two adults could sit in the back seats, but they couldn't be very big adults or their coiffures will be scrubbing up on the roof lining and their genoux polishing the backs of the front seats.

That it's a ferociously powerful, nimble and deeply satisfying car to drive is beyond doubt, and I'd be a very proud man if I owned an RS 5, but it's not a car with much distinctive character or feeling inside where you and your passengers are. Similar knobs and controls for the sound and navigation systems can be found on other more prosaic Audi models, and pretty well all of the general layout should be a familiar place to owners of its lesser contemporaries. It does the job extremely well, but there's nothing indoors or out to make you feel special or emotional when you're just pootling through town.

But hey, it whirrs and thrums with shiny technology and just reading out the executive summary of its multi-hyphen main points sounds like an Autobot Transformer shape-shifting – electrohydraulically-controlled multi-plate clutch, permanent all-wheel drive with self-locking crown-gear differential and torque vectoring, mapped ignition with solid-state high-voltage distribution. Isn't it all just fabby?

Truth is, I'm a big fan of its understated superiority and clutter-free efficiency, I'm enticed by the cocktail of refinement and stealth, seduced by its suave sophistication and thinly disguised capability for brutal violence. And the exhaust note alone is a soundtrack worth owning.

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